As a second time grower, I would say phosphorus deficiency which can occur easily with wrong PH levels. I'm sure more experienced growers will help and comment so please don't do anything without hearing them out :) Yes, wrong PH levels will block the many nutrient uptake and yes it can be...
Yes, I usually add all my fertilizers then wait for like 1-2 mins, then check its PH. BTW I'd like to thank you because after you asked if I have a reliable PH meter, I checked some botteled water PHs (You know, its always written on the label) The PH reading was crazy, it supposed to be 6.6 but...